The present invention relates to composite filtration membranes, methods of their preparation, and uses thereof, and more specifically, to anti-fouling membranes for ultrafiltration comprising a layer of interfacially crosslinked poly(meth)acrylates and/or poly(meth)acrylamides.
Membrane technologies such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) are widely used for water purification because they are energy efficient, cost-effective and simple to operate. However, many commercial membranes experience substantial flux declines when they are exposed to a mixture of inorganic salt, emulsified oil droplets, and natural organic matters (dissolved organic compounds, various proteins, and other bio-materials). These contaminants in water cause membrane fouling (deposition on membrane surface and/or blocking membrane pores), shortening the lifetime of the membrane. Current approaches to address the fouling problem include pretreatment of the feed, periodic depressurization of the membrane tube, flow reversal, and use of cleaning agents to remove fouled films from the membrane surface. These techniques require additional energy and reduce the productive operating time of the membrane, thereby directly contributing to operating cost.
Various materials and methods have also been used to modify membrane surfaces in an effort to enhance fouling resistance. These include coating membrane surfaces with nanoparticles, enzymes, and epoxy compounds; coating membrane surfaces with poly(ethylene glycol) (PEG) based brush copolymers made by atom transfer radical polymerization (ATRP); forming a crosslinked coating based on cyclooctene monomers comprising PEO chains; growing sulfobetaine methacrylate (SBMA) copolymers by ATRP polymerization initiated on a membrane surface; covalently grafting poly(ethylene oxide) (PEO) derivatives comprising epoxy groups to a membrane surface; and employing interfacial polymerization of a difunctional aromatic amine monomer with a multifunctional acid chloride monomer to form a crosslinked polyamide network on a polysulfone UF support for reverse osmosis and nanofiltration membranes, but commercial RO and NF membranes made by interfacial polymerization do not yet provide fouling resistance. The monomers are coated in tandem layers and react without a drying step. Although the above-described materials and techniques are efficient in reducing membrane fouling, generally they are not well-suited for large scale manufacturing. The methods of preparing the modified membranes often require additional steps of casting, drying and curing to form thin selective layers on support membranes. For example, the ATRP based polymers are disadvantaged by the use of a copper catalyst, which is removed at the end of the reaction by passing the ATRP polymers through alumina columns multiple times. In another example, azide-functional cyclooctene monomers, used in making ultraviolet radiation crosslinkable polymers on UF support, are particularly hazardous for large scale industrial applications.
Consequently, a continuing need exists for filtration membranes, particularly for water purification, having enhanced fouling resistance, anti-microbial properties, and/or enhanced salt rejection properties.